There are many different variants of power trains for vehicles. It is often desirable that heavy vehicles be drivable as comfortably as possible for the driver. This means, for example, that the gear changes of the gearbox should be executed automatically by the control system usually incorporated in the vehicle. Gearboxes which change gear automatically are therefore also usual in heavy vehicles.
Generally speaking, in driving of heavy vehicles such as trucks, buses and the like, vehicle economy has over time become an ever greater factor in the profitability of the activity in which the vehicle is used. Apart from its procurement cost, the main costs involved in routine operation of a heavy vehicle normally comprise pay for the driver, repair and maintenance costs, and fuel for propulsion of the vehicle.
Depending on the type of vehicle, the impact of different factors may vary, but fuel consumption is generally a major item of expenditure. Since the capacity utilization of heavy vehicles is often high, involving large overall fuel consumption, every possible way of reducing fuel consumption has a positive effect on profitability. One way of achieving this is to influence the way in which the control system makes gear choices and controls gear changes in the gearbox. For this reason, the control system often incorporates functions for improving fuel consumption by as far as possible effecting gear changes and making gear choices in as fuel-economizing a way as possible.
A certain measure of driver influence may in many situations be desirable, e.g. when it is necessary to change down to a lower gear than the vehicle's control system would otherwise have chosen. Automatic gear changing in heavy vehicles being usually controlled by a control system provides a possibility, which is therefore also often applied, of a mode of control whereby engine and gearbox control, and gear choice, are largely conducted by the control system alone but with a possibility, at least in certain situations, of gear choice being at least partly based also on commands from the vehicle's driver.
In general, the aforesaid automatic gear choice works well in many cases, but there are situations where gear choice by control system may lead to driver irritation. There therefore still are situations in which automatic gear choice can be further improved.